1. Field of the Invention
The present invention relates to a lens barrel equipped with an interlocking key member for, when performing a focusing or zooming operation, transferring a torque needed for this operation.
2. Related Background Art
FIG. 1 is a view illustrating one example of a conventional lens barrel.
A fixed drum 1 includes a mount member 1a provided at the rear end thereof but joined to an unillustrated camera body, an internal cylindrical portion 1b and rectilinear grooves 1c, 1d each formed in the internal cylindrical portion 1b and extending in an optical-axis direction L. This fixed drum 1 inhibits each of a cam ring 2, a zoom operation ring 3 and a segment gear ring 4 from moving in the optical-axis direction L but supports these rings to permit their rotation about the optical axis L.
The cam ring 2 is fixedly connected to a protrusion 3a extending toward an inside diameter of the zoom operation ring 3 but rotates integrally with the zoom operation ring 3.
The segment gear 4 has a segment gear portion 4b formed in an internal peripheral portion at its rear end, which gear portion 4b meshes with a last gear 14 of a gear train linked to an unillustrated driving force source provided in the camera body or in the lens barrel.
Slide drums 5 and 6 are so inserted as to be slidable on an inner peripheral surface of the internal cylindrical portion 1b of the fixed drum 1 and individually have pins 7, 8 formed on their outer peripheral portions. These pins 7, 8 are inserted into cam grooves 2a, 2b formed in the cam ring 2 as well as into the rectilinear grooves 1c, 1d so formed in the internal cylindrical portion 1b of the fixed lens barrel 1 as to extend in the optical-axis direction L.
The slide drum 5 includes a male helicoid thread 5a formed on the front edge thereof. This slide drum 5 inhibits an annular ring 9 from moving in the optical-axis direction L but supports it to permit rotations about the optical axis L.
The slide drum 6 holds a rear lens unit optical system G2.
An interlocking key 10 is fixed to the annular ring 9 with a screw 11 from the optical-axis direction L. This interlocking key 10 is inserted in a key way 4a so formed in the segment gear ring 4 as to extend in the optical-axis direction L. Dimensions of the interlocking key 10 and the key way 4a are set so that the interlocking key 10 does not disengage from the key way 4a with a movement of the slide drum 5 in the optical-axis direction during a zooming operation which will be mentioned later.
A manual focus operation ring 12 is fixed to the annular ring 9 with a screw 13 from a direction orthogonal to the optical axis L.
A lens holding ring 15 serves to hold a front lens unit optical system G1 and is formed with a female helicoid thread 15a formed in the internal surface of the outer cylindrical portion. The female helicoid thread 15a meshes with the male helicoid thread 5a of the slide drum 5. A key protrusion 15b formed on an outer peripheral portion of this lens holding ring 15 engages with a key way 12a so formed in an internal peripheral portion of the manual focus operation ring 12 as to extend in the optical-axis direction L.
Next, an operation of this lens barrel will be explained.
To start with, when the zoom operation ring 3 is rotated when performing the zooming operation, the cam ring 2 rotates together with this ring 3. At this time, the slide drum 5 (as well as the lens holding ring 15 and the optical system G1) and the slide drum 6 (and the optical system G2) move straight back and forth by a predetermined quantity along the optical axis L by the action of the cam grooves 2a, 2b of the cam ring 2, the action of the rectilinear grooves 1c, 1d of the fixed drum 1 and the action of the pins 7, 8 inserted in these grooves.
In case of the auto-focusing, the driving torque of the unillustrated driving force source (motor, etc.) is transferred to the annular ring 9 and the manual focus operation ring 12 from the unillustrated gear train with the gear 14 disposed last via the segment gear portion 4b, the key way 4a and the interlocking key 10.
When the manual focus operation ring 12 is rotated, the lens holding drum 15 (optical system G1) moves back and forth while rotating with the engagements of the key protrusion 15b with the key way 12a and of the male helicoid thread 5a with the female helicoid thread 15a.
In case of the manual focusing, the manual focus operation ring 12 is manually rotated, in the same way as above-mentioned, and the lens holding drum 15 (optical system G1) moves back and forth.
According to the prior art described above, the annular ring 9 can not secure its thickness enough to fix the interlocking key 10 thereto by use of the screw 11 with a strength durable against the above-mentioned transfer of the driving force because of its installation allowable space. The annular ring 9 can not be therefore composed of plastic and is, in many cases, formed as nothing but a metallic member.
On the other hand, the manual focus operation ring 12 is fixed to the annular ring 9 with the screw 13 but is formed of plastic due to constraints in terms of problems of product weight and machining cost.
That is, in the majority of cases, the annular ring 9 and the manual focus operation ring 12 are hindered from being integral with each other for the reason of acquiring a reliability of its strength as well as of the fixed structure of the interlocking key 10.
Further, the screw 11 serves to fix the interlocking key 10 but is a factor of increasing the cost for the operation of fixing the interlocking key 10 to the annular ring 9 by use of screws 11 in addition to the circumstances explained above as well as being, as a matter of course, a high part unit price.